docs: admin: unicode: update information on state of lanana.org document

Replace link to a non-existing page with a note that lanana.org does not
maintain Linux Zone Unicode Assignments anymore.

Remove the reference to H. Peter Anvin and the unicode lanana.org email as
the maintainer of this file, as at this point, this is all maintained by
the general kernel community.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20230307144000.29539-3-lukas.bulwahn@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/unicode.rst

@@ -3,11 +3,10 @@ Unicode support
 
 		 Last update: 2005-01-17, version 1.4
 
-This file is maintained by H. Peter Anvin <unicode@lanana.org> as part
-of the Linux Assigned Names And Numbers Authority (LANANA) project.
-The current version can be found at:
-
-	    http://www.lanana.org/docs/unicode/admin-guide/unicode.rst
+Note: The original version of this document, which was maintained at
+lanana.org as part of the Linux Assigned Names And Numbers Authority
+(LANANA) project, is no longer existent.  So, this version in the
+mainline Linux kernel is now the maintained main document.
 
 Introduction
 ------------